Appendix; Atm: An Overview; Physical Layer; Figure C-1 B-Isdn Model - Cisco BPX-BXM-155-8DX Installation And Configuration Manual

ATM: An Overview

This chapter is an overview of Asynchronous Transfer Mechanism (ATM) on the BPX 8600 Series.
ATM transmits broadband information using fixed length, relatively small, 53-byte cells suitable for
carrying both constant rate data (such as, voice and video) as well as bursty data.
ATM evolved from the Broadband Integrated Services Digital Network (B-ISDN) standard, which in
turn is an extension of ISDN. ISDN defines service and interfaces for public telecommunications
networks.
B-ISDN utilizes a 7-layer reference model similar to the Open Systems Interconnection (OSI) 7-layer
architecture. ATM redefines the lower three levels as shown in Figure C-1. These are the Physical
Layer, the ATM layer, and the ATM Adaptation Layer (AAL).
Figure C-1

Physical Layer

The physical layer is divided into two parts:
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001
B-ISDN Model
Management plane
Control plane User plane
Higher layer functions
AALs
Convergence sublayer
(CS)
(ATM
adaptation
SAR
layers)
ATM layer
TC
Physical
layer
PM
A P P E N D I X
Service specific, e.g., FR-SSCS
Common part convergence
sublayer CPCS
Segmentation and reassembly
Cell header insert/extract
Cell multiplexing/demultiplexing
VPI/VCI addressing and translation
Generic flow control
Transmission convergence
Physical medium
Cisco BPX 8600 Series Installation and Configuration
C
C-1